Preparing viscose rayon



aqueous acid solution containing zinc sulfate.

3,031,256 Patented Apr. 24,1962

PREPARING VISCOSE RAYON Byron A. Thumm, Delaware County, Pa, assignor to American Viscose Corporation, Philadelphia, Pa., :1

. corporation of Delaware p v No Drawing. Original application Apr. 23, 1956, Ser. No. 579,768, now PatentNo. 2,920,973, dated Jan. 12, 1960. Divided and this application Sept. 23, 1959, Ser. No. 841,696 4 8 Claims. (Cl.-18--54) particularly to filaments and fibers of regenerated cellulose from viscose. l l

In the conventional methods of producing shaped bodies "of regenerated cellulose from viscose, a suitable cellulosic material such as'purified cotton linters, wood pulp, mixtures thereof, and thelike is first converted to an alkali cellulose by treatment with a caustic soda solution and after shredding the'treated cellulose material, it is allowed to age. Theagedalkali cellulose is then converted to a xanthate by treatment with carbon disulfide. The cellulose xanthate is subsequently dissolved in a caustic soda solution in an amount calculated to provide a viscose of the desired cellulose and alkali content. After filtration, the viscose solution is allowed to ripen and is subsequently extruded througha shaped orifice into a suitable coagulating and regenerating bath.

In the production of shaped bodies such as filaments, the viscose solution is extruded'through a spinneret into a coagulating and regenerating bath consisting of an The filament may subsequently be passed through a hot aqueous bath where it is stretched to improve its properties such as tensile strength. The filament may then be passed through a dilute aqueous solution of sulfuric acid and sodium sulfate to complete the regeneration of the cellulose, in case it is not completely regenerated upon leaving the stretching stage. The filament is subsequently subjected to washing, purification, bleaching, possibly other treating operations and drying, being collected either before or after these treatments.

The filaments as formed by the conventional methods, consist of a skin or outer shell portion and a core portion with a sharp line of demarkation between the two. The cross-section of the filaments exhibits a very irregular or crenulated exterior surface when even small amounts of zinc salts or certain other polyvalent metal salts are present in the spinning'bath. The skin and core portions of the filament represent differences in structure and these different portions possess difierent swelling and staining characteristics, the latter permitting a ready identification of skin and core. The sharply irregular and crenulated surface structure has a relatively low abrasion resistance and readily picks up foreign particles such as dirt. Although the core portion possesses a relatively high tensile strength, it has a low abrasion resistance and a low flex-life, is subjected to fibrillation and is relatively still. I

It has now been discovered that the presence of small amounts of alkali-soluble reaction products of N,N'-2- ethyl-butyramido ethylene diamine with an alkylene oxide in viscose results in the production of shaped bodies of regenerated cellulose such as filaments, films, sheets and the like composed of all skin and having improved properties and characteristics providingthat the amount of the ester is maintained with certain limits and the composition of the spinning bath is maintained within certain composition limits which will be defined hereinafter. The most readily distinguishable characteristics as compared to conventional filaments include a smooth, non-crenulatedfsurface and the filaments consist entirely of skin;

and butylene oxides. It is obvious that for'all practical of the cellulose.

purposes considering cost, ease of preparation, commercial availability and solubility in water and alkali solutions such as a 6% caustic solution, the ethylene oxide adducts are preferred. Accordingly, the invention will be illustrated by reference to the ethylene oxide adducts.

-The alkylene oxide such as ethylene oxide'content of the adducts'or reaction products should be at least 2 and may vary' up to aboutS alkylene oxide such as ethylene oxide units per molecule of N,N'-2-ethyl butyramido ethylene diamine. The production of all skin products requires that certain minimum amounts of the adduct be in solution in the viscose. The adduct may be conveniently added to the viscose in the form of a solution in alkali or inwater.

The amount of the adduct or reaction product which is incorporated in the viscose must be at least about 0.3% by weight of the cellulose and may vary up to about 3%, preferably, the amount varies from about 0.5%, to 2%. Lesser amounts do not result in the production of products consisting entirely of skin and greater amounts affect adversely the physical properties of the products. Amounts within the preferred range are most effective in enhancing the characteristics and properties of the products. The adduct may be added at any desired stage in the production of the viscose such as in the preparation of the refined wood pulp for the manufacture of viscose,

before or during shredding of the alkali cellulose, to the xanthated cellulose while it is being dissolved in the caustic solution or to the viscose solution before or after filtration. The adduct is preferably added after the cellulose xanthate has been dissolved in the caustic solution and prior to filtration.

The viscose may contain from about 4% to about 10% cellulose, the particular source of the cellulose being selected for the ultimate use of the regenertaed cellulose product. The caustic soda content may be from about 4% to about 8% and the carbon disulfide content may be from about 30% to about 50% based upon the weight The modified viscose, that is, a viscose containing the small amount of the ester may have a sodium chloride salt test above about 8 and preferably about 9 or higher at the time of spinning or extrusion. Referencesherein to the salt test and salt point designate the conventional sodium chloride salt test.

'In order to obtain the improvements enumerated hereinbefore, it is essential that the composition of the spinning bath be maintained within a well defined range. The presence of the esters in the viscose combined with these limited spinning baths results in the production of yarns of improved properties such as high tenacity, high abrasion resistance, high fatigue resistance and consisting of filaments composed entirely of skin.

Generically and in terms of the industrial art, the spinning bath is a low acid-high zinc spinning bath. The bath should contain from about 10% to about 25% sodium 70 C. In the production of the all skin type filaments, the temperature of the spinning bath is not critical, however, as is well known in the conventional practice in the art, certain of the physical properties such as tensile strength vary directly with the temperature of the spinning bath. Thus, in the production of filaments for tire cord purposes in accordance with the method of this invention, the spinning bath is preferably maintained at a temperature between about 55 C. and 65 C. so as to obtain the desired high tensile strength.

The acid content of the spinning bath is balanced against the composition of the viscose. The lower limit of the acid concentration, as is well known in the art, is just above the slubbing point, that is, the concentration at which small slubs of uncoagulated viscose appear in the strand as it leaves the spinning bath. The slubbing point for any specific viscose solution is in accord with usual practice determined by visual observation. For commercial operations, the acid concentration is generally maintained about 0.4% to 0.5 above the slubbing point. For any specific viscose composition, the acid concentration of the spinning bath must be maintained above the slubbing point and below the concentration at which the neutralization of the caustic of the viscose is suiiiciently rapid to form a filament having a skin and core. This maximum acid concentration may be determined by visual observation of the filaments. Thus, the permissible acid content of the bath may be regulated solely by visual observation without analysing the bath to determine the amount of acid present.

There is a maximum acid concentration for any specific viscose composition beyond which the neutralization is sufliciently rapid to produce filaments having a skin and core. For example, in general, the acid concentration of the spinning baths which are satisfactory for the commercial production of the all skin products from a 7% cellulose, 6% caustic viscosecontaining the adduct lies between about 5% and about 8.5%. The acid concentration may be increased as the amount of adduct is increased and also as the salt test of the viscose is increased. There is an upper limit, however, for the acid concentration based upon the amount of adduct and the concentration of caustic in the viscose. -All skin products cannot be obtained if the acid content of the bath is increased above the maximum value although the amount of added adduct is increased beyond about 3% while other conditions are maintained constant. For example, a viscose containing about 7% cellulose, about 6% caustic soda, about 36% (based on the weight of the cellulose) carbon disulfide and 1% (based on the weight of the cellulose) of an adduct as described hereinabove containing 2 ethylene oxide units per molecule and having a salt test of 9 to 9.5 when extruded into spinning baths containing 16% to 20% sodium sulfate, 4% to 8% zinc sulfate and sulfuric acid not more than about 8%, results in the production of all skin filaments. Lesser amounts of sulfuric acid may be employed. Greater amounts of acid result in the production of products having skin and core. It has been determined that the maximum permissible acid content of the bath in practicing the present invention is approximately 9%. A lowering of the amount of adduct, the lowering of the caustic soda content or the lowering of the salt test of the viscose reduces the maximum permissible acid concentration for the production of all skin filaments.

The presence of the adduct in the viscose retards the coagulation and, therefore, the amount of adduct employed must be reduced at high spinning speeds. Thus, for optimum physical characteristics of an all skin yarn formed from a viscose as above and at a spinning speed of about 50 meters per minute, the adduct is employed in amounts within the lower portion of the range, for example, about 0.75%. The determination of the specific maximum and optimum concentration of acid for any specific viscose, spinning bath and spinning speed is a matter of simple experimentation for those skilled in the art. The extruded viscose must, of course, be immersed or maintained in the spinning bath for a period suflicient to effect relatively complete coagulation of the viscose, that is, the coagulation must be sufiicient so that the filaments will not adhere to each other as they are brought together and withdrawn from the bath.

In the production of filaments for such purposes as the fabrication of tire cord, the filaments are preferably stretched after removal from the initial coagulating and regenerating bath. From the initial spinning bath, the filaments may be passed through a hot aqueous bath which may consist of hot water or a dilute acid solution and may be stretched from about 70% to about 110%, preferably between 75% and Yarns for other textile purposes may be stretched as low as 20%. The precise amount of stretching will be dependent upon the desired tenacity and other properties and the specific type of product being produced. If desired, the filaments may be stretched in air. It is to be understood that the invention is not restricted to the production of filaments and yarns but it is also applicable to other shaped bodies such as sheets, films, tubes and the like. The filaments may then be passed through a final regenerating bath which may contain from about 1% to about 5% sulfuric acid and from about 1% to about 5% sodium sulfate with or without small amounts of zinc sulfate if regeneration has not previously been completed.

The treatment following the final regenerating bath, or the stretching operation where regeneration has been completed, may consist of a washing step, a desulfurizing step, the application of a finishing or plasticizing material and drying before or after collecting, or may include other desired and conventional steps such as bleaching and the like. The treatment after regeneration will be dictated by the specific type of shaped body and the proposed use thereof.

Regenerated cellulose filaments prepared from viscose containing the small amounts of the alkali-soluble adducts or reaction products and spun in the spinning baths of limited acid content have a smooth or non-crenulatcd surface and consist substantially entirely of skin. Because of the uniformity of structure throughout the filament, the swelling and staining characteristics are uniform throughout the cross-section of the filament. Filaments produced pursuant to this invention and consisting entirely of skin have a high toughness and a greater flexing life which may be attributed by the uniformity in skin structure throughout the filament. Although the twisting of conventional filaments, as in the production of tire cord, results, in an appreciable loss of tensile strength, there is appreciably less loss in tensile strength in the production of twisted cords from the filaments consisting entirely of skin. Filaments prepared from viscose containing the adducts have a high tensile strength as compared to normal regenerated cellulose filaments, have superior abrasion and fatigue resistance characteristics and have a high flex-life. Such filaments are highly satisfactory for the production of cords for the reinforcement of rubber products such as pneumatic tire casings, but the filaments are not restricted to such uses and may be used for other textile applications.

The invention may be illustrated by reference to the preparation of regenerated cellulose filaments from a viscose containing about 6.7% cellulose, about 5.9% caustic soda, and having a total carbon disulfide content of about 36% based on the weight of the cellulose. The viscose solutions were prepared by xanthating alkali cellulose by the introduction of 36% carbon disulfide, based on the weight of the cellulose, and churning for about 2 /2 hours. The cellulose xanthate was then dissolved in caustic soda solution. The viscose was then allowed to ripen for about 28 horns at 18 C. In those instances where an ester was incorporated in the viscose, the desired amount of the adduct was added to the viscose and mixedfor vabout 16 hour before allowing the ripen. v

In cachinstance, the viscose was'extruded through a spinneret to form a 100 filamentyarn having a-denier and'at a-rate-set forth-in the table'which'follows. The

coagulating and regenerating bath was maintained at a temperature of about 60 C. The yarn after removal I from the spinning bath was passed through a hot water Example I II III IV V VI VII VIII lscose:

Percentadduct... a 1 2 2 0.5 ;1 0.5 1 SaitTest 11.2 11.2 11.2 11.2 9.4 9.4 9.4 9.4 a

PerceutHfiOu--- 8.2 8.2 8.2 8.2 8.4 8 8 8 PeroentZnS04 6 6 -6 6- 6 6 5 PercentNaaS04.-. 16 p, 16 16 16 15 g 15 15 15 Den 200 210 210 210. 230 225 225 230 22 22 22 22 36 36 36 36 83 83 83 83 76 76 l- 76 76 3.2 3.6 3.4 3.5 2.9 2.7 2.7 2.7 2.3 2.7 2.5 2.6 1.9 1.6 1.9 1.8

No'rn.Adducts or reaction products in viscose of: Examples II, III and VI 2 ethylene oxide units/molecule N,N -2-eth l-butyrumido ethylene diamine. :Exum les IV: VII, and VIII, 4 ethylene oxide units/molecule N. '-2-ethyl-butyramido ethylene diamine. Spi n 'speedspeed of extrusion of viscose in meters per in nu e.

ry and T. wet-Tensile strength of dry and wet yarn, Y

' 'I. d res ectivei in ams er denier.

y and E. wet. ercent elongation of dry and wet yarn, respectively.

f. The individual filaments formed in accordance with this'invention have a smooth, non-crenulated exterior surface and consist entirely of skin, no core being detectableathigh magnification (e.g. i500x). .The filaments of the vcontrol'yarn (Example 1) formed from the same accordance with this invention do not exhibit improvements in tensile strength and elongation, however, the

products consist ofa smooth-surfaced, all skin structure and possess improved abrasion resistance, flex-life and other properties disclosed hereinbefore.

One of the properties of viscose rayon which has limited its uses is its relatively high cross-sectional swelling when wet with water, this swelling amounting to from about 65% to about 80% for rayon produced by conventional methods. Rayon filaments produced in accordance with the method of this invention have an appreciably lower cross-sectional swelling characteristic, the swelling amounting to from about 45% to about 60%.

If desired, smallamounts of the adduct may be added to the spinning bath. Since the adducts arewater-soluble, some of the modifier will be leached from the filament or other shaped body and will be present in the bath.

viscose to 6 to produce a viscose'having the-proper proportion of the additive at the time of spinning.

The termskin:is employed to 'designatethat portio of regenerated cellulose filaments which is permanently stained or dyed by the following procedure: A microtome section of one or more of the filaments mounted in a wax block is taken and mounted on a slide with Meyers albuminfixative. After 'dewaxing in xylene, the section is placed in successive baths of and 30% alcohol for a few moments each, and it'isthen stained in 2% aqueous solution of Victoria Blue BS conc. (General Dyestuffs Corp.) for l to 2-hours. Atthis point, the entire section is blue. By rinsing the section first in distilled water and then in one or more baths composed of 10% water'and 90% dioxane for a period varying'from 5 to 30 minutes depending on the particular filament, the dye is entirely removed fromthe core, leavin'g it'restricted' to the skin areas. I l

The term adduct" is used herein synonymously with reaction products and designates the substances formed by reacting an alkylene oxide with N,N'-2'-ethyl-butyramido ethylene diamine wherein the amino hydrogen atoms are replaced with at least one hydroxyalkylene radical or a hydroxypolyoxyalkylene radical, as described hereinbefore.

This application is a division of my copending application Serial No. 579,768, now patent No. 2,920,973, filed April 23, 1956, entitled Preparing Viscose Rayon.

While preferred embodiments of the invention have been disclosed, the description is intended to be illustrative and it is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined by the appended claims.

I claim:

1. In .a method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin, the steps which include extnldin'g viscose containing from about 0.31% to about 3%, based on the weight of the cellulose in the viscose, of an alkali-soluble reaction product of an alkylene oxide with N,N-2-ethyl-butyramido ethylene diamine, the reaction product containing between about 2 and about 5 alkylene oxide units per molecule of N,N'-2-ethylbutyramido ethylene diamine into an aqueous spinning bath containing from about 10% to 'about 25% sodium sulfate, from about 3% to about 15% zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point but not exceeding about 9%.

2. The steps in the method as defined in claim 1 wherein the reaction product is an ethylene oxide reaction product.

3. In a method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin,

the steps which include extruding a viscose containing The adducts may be added to any desired viscose such as those normally used in industry, the specific viscose composition set forth above, being merely for illustrativepurposes. The adducts or reaction products may be from about 4% to about 10% cellulose, from about 4% to about 8% causticsoda, f om about 30% to about 50% carbon disulfide, based on the weight of the cellulose, and from about 0.5% to about 2%, based on the weight of the cellulose in the viscose, of an alkali-soluble reaction product of an alkylene oxide with N,N'-2-ethyl-butyramido ethylene diamine, the reaction product containing between about 2 and about 5 alkylene oxide units per molecule of N,N'-2-ethylbutyramido ethylene diamine into an aqueous spinning bath containing from about 10% to about 25% sodium sulfate, from about 3% to about 15% zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point but not exceeding about 9%, removing the body from the spinning bath and collecting the body.

4. The steps in the method as defined in-claim 3 wherebased upon the weight of the cellulose,

in the reaction product is an ethylene oxidereaction product. I

5. The steps in a method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin which comprise addingto and incorporating in a viscose from about 0.3% to about 3%, based on the weight of the cellulose in the viscose, of an alkali-soluble reaction product of an alkylene oxide with N,N'-2-ethy1- butyramido ethylene diamine, the reaction product containing between about 2 and about 5 alkylene oxide units per molecule of N,N'-2-ethyl-butyramido ethylene diamine,'the viscose containing from about 4% to about 10% cellulose, from about 4% to about 8% caustic soda and from about 30% to about 50% carbon disulfide, and extruding the viscose into an aqueous spinning bath containing from about 10% to about 25% sodium sulfate, from about 3% to about 15% zinc sulfate and sulfuric acid, the sulfuric acid content of the bath exceeding the slubbing point but not exceeding about 9%.

6. The steps in the method as defined in claim 5 wherein the reaction product is an ethylene oxide reaction product.

7. The steps in a method of producing shaped bodies 1 6% caustic soda and about 36% carbon of regenerated cellulose consisting substantially entirely of skin which comprise adding to and incorporating in a viscose from about 0.5% to about 2% of an alkalisoluble reaction product of an alkylene oxide with -N,N' Z-ethyl-butyramido ethylene diamine, containing between about 2 and about 5 alkylene oxide units per molecule of N,N-2-ethyl-butyramido ethylene diamine, the viscose containing about 7% cellulose, about disulfide, based upon the weight of the cellulose, ripening to viscose to a sodium chloride salt point of not less than 9 and extruding the viscose into an aqueous spinning bath containing from about 16% to about 20% sodium sulfate, from about 4% to about 9% zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point but not exceeding about 9%.

8. The steps in the method as defined in claim 7 wherein the reaction product is an ethylene oxide reaction product.

2,910,341 Cox Oct. 27 1959 the reaction product 

1. IN A METHOD OF PRODUCING SHAPED BODIES OF REGENERATED CELLULOSE CONSISTING SUBSTANTIALLY ENTIRELY OF SKIN, THE STEPS WHICH INCLUDE EXTRUDING VISCOSE CONTAINING FROM ABOUT 0.3% TO ABOUT 3%, BASED ON THE WEIGHT OF THE CELLULOSE IN THE VISCOSE, OF AN ALKALI-SOLUBLE REACTION PRODUCT OF AN ALKYLENE OXIDE WITH N,N''-2-ETHYL-BUTYRAMIDO ETHYLENE DIAMINE, THE REACTION PRODUCT CONTAINING BETWEEN ABOUT 2 AND ABOUT 5 ALKYLENE OXIDE UNITS PER MOLECULE OF N,N''-2-ETHYLBUTYRAMIDO ETHYLENE DIAMINE INTO AN AQUEOUS SPINNING BATAH CONTAINING FROM ABOUT 10% TO ABOUT 25% SODIUM SULFATE, FROM ABOUT 3% TO ABOUT 15% ZINC SULFATE AND SULFURIC ACID, THE SULFURIC ACID CONTENT OF THE SPINNING BATH EXCEEDING THE SLUBBING POINT BUT NOT EXCEEDING ABOUT 9%. 